WO2019022358A1 - Cathode for lithium-sulfur battery, and lithium-sulfur battery comprising same - Google Patents

Abstract

The present invention relates to a cathode for a lithium-sulfur battery, and a lithium-sulfur battery comprising the same and, more specifically, to a cathode for a lithium-sulfur battery, comprising an active material, a conductive material, a binder and an additive, wherein the additive is an organic acid lithium salt containing a dicarboxyl group. The cathode for a lithium-sulfur battery comprises an organic acid lithium salt containing a dicarboxyl group as the additive, and thus improves the movement characteristics of lithium ions, thereby enabling capacity and lifespan characteristics of a lithium-sulfur battery to be improved.

Description

Lithium-sulfur battery anode and lithium-sulfur battery containing the same

This application claims the benefit of priority based on Korean Patent Application No. 10-2017-0096485, filed on July 28, 2017, the entire contents of which are incorporated herein by reference.

The present invention relates to a positive electrode for a lithium-sulfur battery and a lithium-sulfur battery including the same.

Recently, electronic devices and communication devices have been rapidly made smaller, lighter, and more sophisticated. As the necessity of electric automobiles has been increased with respect to environmental problems, improvement of the performance of secondary batteries, which can be used as energy sources for these products, have. Many studies have been made on a lithium-sulfur battery using a sulfur material as a cathode active material as a secondary battery satisfying such demands.

The lithium-sulfur battery uses a sulfur-based compound containing a sulfur-sulfur bond as a cathode active material and a carbon-based material in which metal ions such as lithium metal or lithium ions are inserted / Tin or the like as a negative electrode active material.

Specifically, the oxidation reaction of lithium occurs at the negative electrode of the lithium-sulfur battery, and the reduction reaction of sulfur occurs at the positive electrode. Sulfur before discharging has an annular S ₈ structure. Reduction of sulfur-sulfur bond during reduction (discharge) reduces the oxidation number of sulfur, and when sulfurization is re-formed during oxidation (charging), oxidation number of sulfur increases The oxidation-reduction reaction is used to store and generate electrical energy.

In particular, the theoretical discharge capacity of a lithium-sulfur battery is 1,675 mAh / g and the theoretical energy density is 2,600 Wh / kg, which is about 5 times higher than the lithium ion battery currently being studied (about 570 Wh / kg) It is possible to realize high capacity, high energy density and long life. In addition, since sulfur, which is the main material of the cathode active material, has a low atomic weight, is easy to supply and demand due to its abundant resources, is low in price, is not toxic and is an environmentally friendly material, lithium- And is attracting attention as an energy source for medium to large-sized devices.

Sulfur used as a cathode active material in a lithium-sulfur battery has an electric conductivity of 5 × 10 ^-30 S / cm, which is an insulator having no electrical conductivity. Therefore, it is difficult to transfer electrons generated by an electrochemical reaction. And is used in combination with a conductive material such as carbon capable of providing an electrochemical reaction site.

On the other hand, in order for sulfur to exhibit sufficient performance in a lithium-sulfur battery, lithium ion conductivity is required along with electric conductivity. However, in the case of a sulfur-carbon composite used as a cathode active material of a conventional lithium-sulfur battery, the lithium ion conductivity is still low, and various techniques have been proposed.

Korean Patent Laid-Open Publication No. 2016-0046775, for example, discloses a positive electrode active portion including a sulfur-carbon composite having a positive electrode coating layer made of an amphipathic polymer on a surface thereof to facilitate dissolution of polysulfide and migration of lithium ions And the cycle characteristics of the battery can be improved.

Korean Patent Publication No. 2002-0066783 discloses that ion conductivity can be increased by including polyethylene oxide (PEO) and an inorganic lithium salt in a sulfur anode for a lithium battery.

These patents have improved lithium ion conductivity to some extent through additives or coatings, but the effect is not sufficient. Therefore, development of a positive electrode for a lithium-sulfur battery having excellent lithium ion conductivity is further required.

[Prior Art Literature]

[Patent Literature]

Korean Patent Laid-Open Publication No. 2016-0046775 (Feb. 26, 2019), a cathode for a lithium-sulfur battery and a method for producing the same

Korean Patent Publication No. 2002-0066783 (Aug. 22, 2002), a sulfur positive electrode for a lithium battery and a method for producing the same

As a result, the present inventors have conducted various studies to solve the above problems. As a result, when the organic acid lithium salt containing a dicarboxylic group is included as an additive in the anode for a lithium-sulfur battery, the conductivity of the lithium ion is improved, The life span is improved, and the present invention has been completed.

Accordingly, an object of the present invention is to provide a positive electrode for a lithium-sulfur battery excellent in performance and life characteristics.

Another object of the present invention is to provide a lithium-sulfur battery including the positive electrode.

In order to achieve the above object, the present invention provides a positive electrode for a lithium-sulfur battery, which comprises an active material, a conductive material, a binder and an additive, wherein the additive is an organic acid lithium salt containing a dicarboxylic group.

The organic acid lithium salt may include an oxalate group or a malonate group.

The organic acid lithium salt may include at least one member selected from the group consisting of di lithium oxalate, lithium hydrogen oxalate, lithium bis oxalate borate, di lithium malonate, lithium hydrogen malonate and lithium bismarnonate borate. have.

The organic acid lithium salt may be contained in an amount of 0.1 wt% or more and less than 5 wt% based on 100 wt% of the entire positive electrode for a lithium-sulfur battery.

In addition, the present invention provides a lithium-sulfur battery including the positive electrode.

The positive electrode for a lithium-sulfur battery according to the present invention includes an organic acid lithium salt containing a dicarboxyl group as an additive, thereby improving the migration characteristics of lithium ions, thereby improving the capacity and lifetime characteristics of the lithium-sulfur battery.

1 is a graph showing charge / discharge characteristics of a battery according to Experimental Example 1 of the present invention.

2 is a graph showing lifetime characteristics of the batteries manufactured in Example 1, Example 3, Example 4, Comparative Example 1 and Comparative Example 3 of the present invention.

3 is a graph showing lifetime characteristics of the battery manufactured in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention.

Hereinafter, the present invention will be described in more detail.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Lithium-sulfur battery has much higher discharging capacity and theoretical energy density than existing lithium secondary batteries, and sulfur, which is used as a cathode active material, is attracting attention as a next-generation battery because of its abundant reserves, low cost, and environment friendliness.

Despite these advantages, the theoretical capacity and the energy density are not realized in actual operation. This is because the low lithium ion conductivity of sulfur, the cathode active material, is very low in the proportion of sulfur participating in the actual electrochemical redox reaction. The capacity and efficiency of the lithium-sulfur battery may vary depending on the amount of lithium ions delivered to the anode. Therefore, it is important to increase the lithium ion conductivity of the positive electrode to increase the capacity and high efficiency of the lithium-sulfur battery.

In addition, in the lithium-sulfur battery, the lithium polysulfide formed in the anode is lost outside the anode reaction region during the charge-discharge reaction, resulting in a shuttle phenomenon of moving between the anode and the cathode. At this time, lithium sulfide is fixed on the surface of the lithium metal due to the side reaction between the lithium polysulfide eluted from the anode and the lithium metal as the negative electrode, so that the reaction activity is lowered and the lithium ion is unnecessarily consumed, A problem arises.

In the prior art, in order to improve the lithium ion conductivity, a method of increasing the lithium salt concentration of the electrolyte or introducing an additive or a coating layer into the electrolyte or the positive electrode has been used, but the performance and lifetime of the lithium-sulfur battery are not effectively improved.

Accordingly, the present invention provides a positive electrode for a lithium-sulfur battery having improved capacity and life characteristics by improving the low lithium ion conductivity of a conventional lithium-sulfur battery anode and improving the reactivity and stability of the electrode.

Specifically, the cathode for a lithium-sulfur battery according to the present invention includes an active material, a conductive material, a binder and an additive, and the additive includes an organic acid lithium salt containing a dicarboxyl group.

In order to improve the lithium ion conductivity in the prior art, the concentration of the lithium salt in the electrolyte is increased or the inorganic / organic lithium salt is added. In particular, the organic lithium salt is used as an additive to the electrolyte for the purpose of forming a protective film or maintaining the performance of the battery However, in the present invention, the organic acid lithium salt is included in the cathode composition rather than the electrolyte.

According to the present invention, the organic acid lithium salt containing the dicarboxylic group is introduced into the anode to secure a certain level of lithium ion concentration in the anode, thereby improving the lithium ion conductivity of the anode. The problem of lowering the reactivity of the anode is solved.

Further, when a large amount of lithium salt is contained in the electrolyte or an inorganic or organic lithium salt is introduced into the electrolyte as an additive, the viscosity of the electrolyte increases and the reactivity such as the transfer of lithium ions in the electrolyte or the dissolution of lithium polysulfide is changed And the capacity and output characteristics of the battery deteriorate. Also, as described above, the composition or the content of the electrolyte changes as the impurities act as the battery cycle progresses, increasing the resistance in the battery and drastically decreasing the capacity and lifetime of the battery. However, according to the present invention, when the organic acid lithium salt is included in the positive electrode, the conductivity of the lithium ion in the positive electrode can be effectively increased without affecting the electrolyte and other battery components. The charge / discharge reaction, It is possible to supplement the consumption of lithium ions caused when the electrolyte is decomposed or a side reaction occurs.

The organic acid lithium salt according to the present invention includes a dicarboxyl group represented by the following formula (1)

[Chemical Formula 1]

(In the formula 1,

R is a single bond or a methanediyl group.

Formula 1 oxalate ^{_{(oxalate, C 2 O 4 2}} -) may be or malonate _{(malonate, CH 2 (C 2} O 4) 2-) , and the oxalate to preferable.

The organic acid lithium salt of the present invention containing the dicarboxylic group of Formula 1 may be selected from the group consisting of dilithium oxalate, lithium hydrogen oxalate, lithium bis (oxalato) borate, dilithium malonate, lithium hydrogen malonate, and lithium bis (malonato) borate. These materials may be used alone or in combination of two or more thereof. . Preferably, it may be at least one member selected from the group consisting of di-lithium oxalate, lithium hydrogen oxalate and di-lithium malonate, more preferably di-lithium oxalate.

The organic acid lithium salt of the present invention is obtained by replacing the hydrogen of the hydroxyl group of the compound containing a dicarboxyl group of the formula (1) with lithium, and contains a large amount of lithium ions in the compound. Therefore, the organic acid lithium salt is a lithium-rich compound. As described above, even when a small amount of the organic acid lithium salt is added only in a small amount, the lithium ion conductivity in the anode can be greatly increased. . In addition, the organic acid lithium salt can maintain a constant lithium ion concentration in the anode even when sulfur is excessively loaded, thereby improving the capacity or reactivity degradation caused by high-loading of sulfur. In addition, since the organic acid lithium salt has a small molecular weight, it does not affect the driving of other components in the battery, and thus is more effective than the conventional electrolyte. In addition, the lithium ion consumed in the charge / discharge reaction, electrolyte decomposition, Thereby preventing a reduction in the life of the battery.

The organic acid lithium salt can be prepared by neutralizing an acid compound having a dicarboxylic acid group represented by the formula (1) with a base compound containing a lithium salt, and a neutralization method can be used as the neutralization method. The base compound may be lithium hydroxide.

The organic acid lithium salt may be contained in an amount of 0.1 to 5 wt.%, Preferably 0.1 to 3 wt.% Based on 100 wt.% Of the positive electrode for a lithium-sulfur battery. If the amount of the organic acid lithium salt contained in the anode is less than the above range, the addition effect is insufficient and the effect of improving the lithium ion conductivity of the anode is small. On the contrary, when the amount exceeds the above range, The performance of the battery may be adversely affected, or the lithium salt of the organic acid in the anode may not be uniformly dispersed. Therefore, it is desirable to determine the optimum content within the above range. However, the specific optimum amount of the organic acid lithium salt can be set differently according to the anode and the other characteristics and the use environment of the battery including the anode, and the use of the organic acid lithium salt is not limited by the preferred range.

Meanwhile, the positive electrode for a lithium-sulfur battery of the present invention includes a sulfur-based compound as an active material. The sulfur-based compound is a mixture of inorganic sulfur (S ₈ ), Li ₂ S _n (n ≥ 1), an organic sulfur compound and a carbon-sulfur polymer [(C ₂ S _x ) _n , x = 2.5 to 50, n ≥ 2] May be at least one selected from the group consisting of Preferably, inorganic sulfur (S ₈ ) can be used.

Since the sulfur-based compound alone does not have electrical conductivity, it is used in combination with a conductive material. Preferably, the active material may be in the form of a sulfur-carbon composite, and the addition of the organic acid lithium salt of the present invention does not affect the sulfur-carbon composite structure retention.

The active material of the present invention may further include at least one additive selected from transition metal elements, Group IIIA elements, Group IVA elements, sulfur compounds of these elements, and alloys of these elements and sulfur in addition to the above-mentioned composition.

The transition metal element may be at least one element selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Hg and the like, and the Group IIIA element includes Al, Ga, In, and Ti, and the Group IVA element may include Ge, Sn, Pb, and the like.

The active material may be contained in an amount of 50 to 95% by weight, preferably 70 to 95% by weight, based on 100% by weight of the positive electrode for a lithium-sulfur battery. If the active material is contained in an amount less than the above range, it is difficult to sufficiently exert the reaction of the electrode. Even if the active material is contained in an amount exceeding the above range, the content of the conductive material and the binder is relatively insufficient, It is desirable to determine the content.

Among the components constituting the positive electrode for a lithium-sulfur battery of the present invention, the conductive material is a material that serves as a path for electrically connecting an electrolyte and an active material to move an electron from the current collector to the active material. Anything you can use without restrictions.

For example, carbon-based materials having porosity can be used. Examples of the carbon-based materials include carbon black, graphite, graphene, activated carbon, carbon fiber, and the like; metallic fibers such as metal mesh; Metallic powder such as copper, silver, nickel, and aluminum; Or an organic conductive material such as a polyphenylene derivative. The conductive materials may be used alone or in combination. Commercially available conductive materials include acetylene black series (Chevron Chemical Company or Gulf Oil Company products), Ketjen Black EC series (Armak Company Vulcan XC-72 (Cabot Company) and Super P (MMM Co., Ltd.).

The conductive material may be contained in an amount of 1 to 10% by weight, preferably 1 to 5% by weight based on 100% by weight of the entire cathode for a lithium-sulfur battery. If the content of the conductive material contained in the anode is less than the above range, portions which are unreactive in the active material in the electrode are increased, resulting in a decrease in the capacity. If the amount is less than the above range, a high efficiency discharge characteristic and an adverse effect on the charge / It is desirable to determine the optimum content within the above-mentioned range.

Among the components constituting the positive electrode for a lithium-sulfur battery of the present invention, the binder is a substance which is contained in the current collector for holding the slurry composition forming the positive electrode, and is well dissolved in the solvent and stable in the conductive network with the above- Is used. All binders known in the art can be used unless otherwise specified. For example, the binder may include a fluororesin binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); Rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxyl methyl cellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; Polyalcohol-based binders; Polyolefin binders including polyethylene and polypropylene; Polyimide-based binders; Polyester binders; And a silane-based binder; and mixtures or copolymers of two or more thereof.

The binder may be contained in an amount of 1 to 10% by weight, preferably 5 to 8% by weight based on 100% by weight of the positive electrode for a lithium-sulfur battery. If the content of the binder is less than the above range, the physical properties of the anode deteriorate and the active material and the conductive material may fall off. On the other hand, if the amount exceeds the above range, the ratio of the active material and the conductive material is relatively decreased, It is desirable to determine the titratable amount within the above-mentioned range.

The positive electrode for a lithium-sulfur battery according to the present invention comprising the above-described organic acid lithium salt, active material, conductive material and binder can be produced by a conventional method.

For example, in the preparation of the positive electrode slurry, a dicarboxylic acid compound is first dissolved in a solvent, and then a base compound containing lithium is added thereto, followed by drying to prepare a powdery organic acid lithium salt. Then, the organic acid lithium salt is mixed with the active material, the conductive material and the binder to obtain a slurry composition for forming the anode. Then, the slurry composition is coated on the current collector and dried to complete the positive electrode. At this time, if necessary, the current collector may be compression molded to improve the electrode density.

As described above, the positive electrode for a lithium-sulfur battery of the present invention has a superior lithium ion conductivity improvement effect by uniformly distributing the organic acid lithium salt in the positive electrode by adding the organic acid lithium salt during the production of the positive electrode slurry composition, So that convenient and efficient manufacture is possible.

The current collector generally has a thickness of 3 to 500 占 퐉 and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, a conductive material such as stainless steel, aluminum, copper, or titanium can be used, and more specifically, a carbon-coated aluminum current collector can be used. The use of a carbon-coated aluminum substrate is advantageous in that it has an excellent adhesion to an active material, has a low contact resistance, and can prevent corrosion caused by aluminum polysulfide, as compared with a carbon-coated aluminum substrate. The current collector may have various shapes such as a film, a sheet, a foil, a net, a porous body, a foam or a nonwoven fabric.

The present invention also provides a lithium-sulfur battery including the positive electrode for a lithium-sulfur battery.

The lithium-sulfur battery includes a positive electrode; cathode; And a separator interposed between the anode and the cathode, and an electrolyte. The anode for a lithium-sulfur battery according to the present invention is used as the anode.

The positive electrode is according to the invention and as described above.

The negative electrode may include a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector. Or the cathode may be a lithium metal plate.

The negative electrode current collector is for supporting the negative electrode active material and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of the lithium secondary battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, Palladium, sintered carbon, surface treated with carbon, nickel, silver or the like on the surface of copper or stainless steel, aluminum-cadmium alloy, or the like can be used.

The negative electrode current collector can form fine irregularities on the surface thereof to enhance the bonding force with the negative electrode active material, and various forms such as a film, a sheet, a foil, a mesh, a net, a porous body, a foam, and a nonwoven fabric can be used.

The negative electrode active material may include a material capable of reversibly intercalating or deintercalating lithium (Li ⁺ ), a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, a lithium metal or a lithium alloy can do. The material capable of reversibly storing or releasing lithium ions (Li ^< ^{+ &} gt ^; ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material capable of reacting with the lithium ion (Li ^< ^{+ &} gt ^; ) to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitride or silicon. The lithium alloy includes, for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg) Ca, strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn). Preferably, the negative electrode active material may be lithium metal, and may be in the form of a lithium metal thin film or a lithium metal powder.

The method for forming the negative electrode active material is not particularly limited, and a layer or a film forming method commonly used in the art can be used. For example, a method such as compression, coating, or deposition may be used. Also, the case where the metal lithium thin film is formed on the metal plate by initial charging after assembling the battery without the lithium thin film in the current collector is also included in the negative electrode of the present invention.

The separation membrane is used to physically separate both electrodes in the lithium-sulfur battery of the present invention, and can be used without any particular limitation as long as it is used as a separation membrane in a lithium-sulfur battery. In particular, It is preferable that the electrolytic solution has excellent water hammer ability.

The separator may be formed of a porous substrate. The porous substrate may be any porous substrate commonly used in an electrochemical device. For example, the porous substrate may be a polyolefin porous film or a nonwoven fabric. .

Examples of the polyolefin-based porous film include polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, and polypentene, such as high-density polyethylene, linear low density polyethylene, low density polyethylene and ultra high molecular weight polyethylene, One membrane can be mentioned.

The nonwoven fabric may include, in addition to the polyolefin nonwoven fabric, for example, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate ), Polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylenesulfide, and polyethylene naphthalate, which are used alone or in combination, Or a nonwoven fabric formed of a polymer mixed with these. The structure of the nonwoven fabric may be a spun bond nonwoven fabric or a melt blown nonwoven fabric composed of long fibers.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm.

The size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.001 to 50 탆 and 10 to 95%, respectively.

The electrolyte is located between the anode and the cathode, and includes a lithium salt and an electrolyte solvent.

The concentration of the lithium salt may be in the range of 0.2 to 2 M, preferably 1 to 2 M, depending on various factors such as the precise composition of the electrolyte solvent mixture, the solubility of the salt, the conductivity of the dissolved salt, the charge and precondition of the cell, Specifically 0.4 to 2 M, more particularly 0.4 to 1.7 M. If the concentration of the lithium salt is less than 0.2 M, the conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. If the concentration exceeds 2 M, the viscosity of the electrolyte may increase and the mobility of the lithium ion may decrease.

The lithium salt can be used without limitation as long as it is commonly used in an electrolyte solution for a lithium-sulfur battery. For example, LiSCN, LiBr, LiI, LiPF 6, LiBF 4, LiB 10 Cl 10, LiSO 3 CF 3, LiCl, LiClO 4, LiSO 3 CH 3, LiB (Ph) 4, LiC (SO 2 CF 3) 3 _{, LiN (SO 2 CF 3)} 2, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, may be included are one or more from LiFSI, chloro group consisting of borane lithium, lower aliphatic carboxylic acid lithium or the like.

The electrolyte solvent may be a non-aqueous organic solvent, a single solvent, or two or more mixed organic solvents. When two or more mixed organic solvents are used, it is preferable to select one or more solvents from two or more of the weak polar solvent group, the strong polar solvent group, and the lithium metal protective solvent group.

The weak polar solvent is defined as a solvent having a dielectric constant of less than 15 which is capable of dissolving a sulfur element in an aryl compound, a bicyclic ether, or a cyclic carbonate, and the strong polar solvent is a bicyclic carbonate, a sulfoxide compound, a lactone compound , A ketone compound, an ester compound, a sulfate compound, and a sulfite compound, wherein the lithium metal protective solvent is a saturated ether compound, an unsaturated ether compound, an N, Is defined as a solvent having a charge / discharge cycle efficiency of 50% or more to form a stable SEI (Solid Electrolyte Interface) on a lithium metal such as a heterocyclic compound containing O, S, or a combination thereof.

Specific examples of the weak polar solvent include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme or tetraglyme .

Specific examples of the strong polar solvent include hexamethyl phosphoric triamide,? -Butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl- Dimethyl formamide, sulfolane, dimethylacetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, or ethylene glycol sulfite.

Specific examples of the lithium protecting solvent include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethylisoxazole, furan, 2-methylfuran, 1,4-oxane or 4-methyldioxolane.

The electrolyte may include at least one selected from the group consisting of a liquid electrolyte, a gel polymer electrolyte, and a solid polymer electrolyte. And may be an electrolyte in a liquid state.

The injection of the electrolytic solution can be performed at an appropriate stage in the manufacturing process of the electrochemical device according to the manufacturing process and required properties of the final product. That is, it can be applied before assembling the electrochemical device or in the final stage of assembling the electrochemical device.

The lithium-sulfur battery according to the present invention can be laminated, stacked, and folded in addition to winding, which is a general process.

The shape of the lithium-sulfur battery is not particularly limited, and may be various shapes such as a cylindrical shape, a laminate shape, and a coin shape.

The present invention also provides a battery module including the lithium-sulfur battery as a unit battery.

The battery module may be used as a power source for medium and large-sized devices requiring high temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the above medium and large-sized devices include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

Examples and Comparative Examples

[Example 1]

4.2 g of sulfur and 1.8 g of carbon nanotubes were uniformly mixed in the reactor and then heat-treated at 155 ° C for 30 minutes to prepare a sulfur-carbon composite.

On the other hand, an aqueous solution of lithium hydroxide was added to an oxalic acid aqueous solution to titrate the solution to a pH of 8, and then dried to prepare a dilithium oxalate.

Thereafter, 86.3 wt% of the sulfur-carbon composite (S: C = 7: 3) prepared as the active material, 4.9 wt% of carbon black as the conductive material, 6.8 wt% of polyacrylic acid (PAA) And 2.0 wt% of the dilithium oxalate thus prepared were mixed to prepare a positive electrode slurry composition.

Then, the slurry composition prepared above was coated on an aluminum current collector and dried at 50 DEG C for 12 hours to prepare a positive electrode.

Thereafter, a coin-type lithium-sulfur battery including a cathode, a separator, a cathode, and an electrolyte prepared according to the above was prepared.

Specifically, the positive electrode was used as a 14-phi circular electrode. The polyethylene (PE) membrane was used at 19 phi and the 150 탆 lithium metal was used at 16 phi as a negative electrode. An electrolyte composed of TEGDME / DOL (dioxolane) / DME (Dimethyl ether) (1: 1: 1), LiN (CF ₃ SO ₂ ) ₂ (LiTFSI) 1M and LiNO ₃ 0.1M was used.

[Example 2]

A lithium-sulfur battery was produced in the same manner as in Example 1 except that di-lithium malonate was used in the same amount instead of dilithium oxalate in the preparation of the positive electrode slurry composition.

[Example 3]

A positive electrode slurry composition was prepared in the same manner as in Example 1 except that 83.2% by weight of a sulfur-carbon composite material, 4.9% by weight of a conductive material, 6.9% by weight of a binder and 5.0% by weight of dilithium oxalate was used. - Sulfur batteries were prepared.

[Example 4]

A lithium-sulfur battery was produced in the same manner as in Example 1 except that lithium succinate was used in the same amount in place of di-lithium oxalate in the preparation of the positive electrode slurry composition.

At this time, the lithium succinate was prepared by adding an aqueous solution of lithium hydroxide to succinic acid aqueous solution to titrate to pH 8 and then drying.

[Comparative Example 1]

The procedure of Example 1 was repeated, except that di-lithium oxalate was not used in the preparation of the positive electrode slurry composition, and sulfur-carbon composite material: conductive material: binder was mixed at a weight ratio of 88: 5: 7, - Sulfur batteries were prepared.

[Comparative Example 2]

The cathode was prepared by mixing the sulfur-carbon composite material: conductive material: binder in a weight ratio of 88: 5: 7 without using dilithium oxalate, except that the dilithoxalate was added in an amount of 0.5 wt% A lithium-sulfur battery was fabricated in the same manner as in Example 1.

[Comparative Example 3]

A lithium-sulfur battery was produced in the same manner as in Example 1 except that lithium citrate was used in the same amount in place of dilithium oxalate in the preparation of the positive electrode slurry composition.

At this time, the lithium citrate was prepared by adding an aqueous solution of lithium hydroxide to an aqueous solution of citric acid to titrate the solution to a pH of 8, followed by drying.

Experimental Example  One. Charging and discharging  Character rating

The capacity of the battery prepared in the above-described Examples and Comparative Examples was measured in a voltage range of 1.8 to 2.8 V using a charge-discharge measuring apparatus. Specifically, discharging / charging was repeated 2.5 times at an initial 0.1 C rate, and the battery was charged and discharged at 0.3 C rate and discharged at 0.5 C rate after repeating charging and discharging three times at 0.2 C rate. did. The results obtained at this time are shown in Fig.

Experimental Example  2. Evaluation of life characteristics

The cells prepared in the above Examples and Comparative Examples were repeatedly discharged / charged 2.5 times at an initial 0.1 C rate, repeatedly charged and discharged three times at a rate of 0.2 C, charged at a rate of 0.3 C and discharged at a rate of 0.5 C repeatedly The non-discharge capacity and the Coulomb efficiency were measured to confirm the lifetime characteristics. The results obtained at this time are shown in Figs.

1 to 3, it can be seen that the life characteristics of the battery including the positive electrode according to the present invention are superior to those of the comparative example.

Specifically, as shown in FIG. 1, it can be confirmed that the charging and discharging characteristics of batteries according to Examples and Comparative Examples are similar regardless of whether additives are used or not. However, in the case of Comparative Example 3 using lithium citrate, it is confirmed that an overvoltage occurs in the initial discharge curve due to the increase in resistance.

On the other hand, in terms of lifetime characteristics, the lifetime characteristics of the battery including the anode of the examples are better than those of the comparative examples, as shown in Figs. 2 and 3.

Concretely, as shown in Fig. 2, as compared with the case of Comparative Example 1 in which the additive is not contained, the rate of abrupt decrease in the capacity from the 90th cycle to the 30th cycle in Comparative Example 3 including the citrate, 1, it is confirmed that the non-discharge capacity is stably maintained after 100 cycles. In addition, it can be seen from FIG. 3 that the non-discharge capacity of Comparative Example 2 using the electrolyte as the additive is steadily reduced as compared with Example 1, and the life characteristics are degraded.

The positive electrode for a lithium-sulfur battery according to the present invention includes an organic acid lithium salt containing a dicarboxyl group as an additive, thereby improving the lithium ion conduction characteristic, thereby enabling high capacity, high stability and longevity of the lithium-sulfur battery.

Claims (6)

1. An active material, a conductive material, a binder, and an additive,

   Wherein the additive is an organic acid lithium salt containing a dicarboxyl group.
2. The method according to claim 1,

   Wherein the organic acid lithium salt comprises an oxalate group or a malonate group.
3. The method according to claim 1,

   Wherein the organic acid lithium salt is at least one selected from the group consisting of di lithium oxalate, lithium hydrogen oxalate, lithium bis oxalate borate, di lithium malonate, lithium hydrogen malonate, and lithium bismaronate borate. Anode for lithium-sulfur battery.
4. The method according to claim 1,

   Wherein the organic acid lithium salt is contained in an amount of 0.1 wt% or more and less than 5 wt% based on 100 wt% of the entire positive electrode for a lithium-sulfur battery.
5. The method according to claim 1,

   Wherein the active material is a sulfur-carbon composite.
6. A lithium-sulfur battery comprising a positive electrode according to any one of claims 1 to 5.

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